While specific details of the Withnail & I actor's role have not yet been confirmed, Grant has previously appeared within the Doctor Who universe as the voice of the Ninth Doctor in the flash-animated series Scream of the Shalka, which featured on the show's website in 2003.

"I played Doctor Who in the digital animated Scream Of The Shalka and I'm honoured to be in the Christmas Special," Grant said in an official statement.

Tom Ward (Silent Witness) will also appear in the festive instalment opposite Matt Smith and new companion Jenna-Louise Coleman, who will make her Doctor Who debut in the episode.

Filming on the Christmas special - under director Saul Metzstein - will commence this week in Wales.

Doctor Who will return with its seventh series premiere 'Asylum of the Daleks' in August. The episode will debut at BFI Southbank in London on August 14, and will also be broadcast at the Edinburgh TV Festival later this month.

However, a television air date for 'Asylum of the Daleks' has not yet been revealed by the BBC.